Matt, UV-stable, Thermoformable, co-extruded polyester film, a method for the production thereof and the use of the same

ABSTRACT

The invention relates to biaxially oriented, co-extruded polyester films. Said films comprise a base layer which consists of at least 70% by weight of a thermoplastic polyester, preferably polyethylene terephthalate (PET) with a diethylene glycol and/or polyethylene glycol content greater than 1.3% by weight and have at least one matt outer layer and optionally additional intermediate layers. The films also contain at least one UV-absorber, preferably hydroxy benzotriazoles and triazines. The films are characterized by high UV-stability, no embrittlement after exposure to temperature, a matt surface devoid of unwanted clouding and excellent thermoforming properties and are, together with the molded bodies produced therefrom, suitable for numerous interior and exterior applications. The (matt) outer layers can be identical or different and contain a mixture or a blend of a component I which consists of PET homopolymers and/or copolymers and a component II which is a copolymer resulting from the condensation product of isophthalic acid, an aliphatic dicarboxylic acid and a sulfomonomer with a copolymerizable aliphatic or cycloaliphatic glycol.

The invention relates to a biaxially oriented polyester film which has abase layer preferably composed of at least 70% by weight of athermoplastic polyester and which is thermoformable, and comprises atleast one UV absorber, and has at least one matt outer layer whichcomprises a mixture or a blend made from two components I and II. Theinvention further relates to the use of the film and to a process forits production.

Component I of the mixture or of the blend is preferably a polyethyleneterephthalate homopolymer or polyethylene terephthalate copolymer or amixture made from polyethylene terephthalate homo- and/or copolymers.

Component II of the mixture or of the blend is a polyethyleneterephthalate copolymer which is composed of the condensation product ofthe following monomers or of their derivatives capable of formingpolyesters: isophthalic acid, aliphatic dicarboxylic acid, sulfomonomerwhich contains a metal sulfonate group on the aromatic moiety of anaromatic dicarboxylic acid, and aliphatic or cycloaliphatic glycol.

The outer layer has a matt surface or appearance. The film of theinvention is highly suitable for use as a packaging film or as amolding, or for applications in the industrial sector, where aparticular requirement is UV protection or impermeability to UV light.

BACKGROUND OF THE INVENTION

There is high industrial demand for transparent, high-gloss plasticfilms, e.g. biaxially oriented polypropylene films or biaxially orientedpolyester films. Alongside this, there is increasingly a requirement forthese transparent films and moldings where protection is afforded fromultraviolet radiation and where at least one surface layer does not havehigh gloss but has a characteristic matt appearance, giving theapplication or the moldings an appearance which is particularlyattractive and therefore effective for promotional purposes, and givingthem protection from UV radiation.

EP 346 647 describes a biaxially oriented polyester film which comprisesat least one outer layer which comprises a concentration of from 0.5 to50% of a filler, the diameter of this filler having a particular ratioto the thickness of the outer layer. The outer layer also has aparticular thickness and a particular degree of crystallization,determined with the aid of Raman spectroscopy.

U.S. Pat. No. 4,399,179 describes a coextruded biaxially orientedpolyester film which is composed of a transparent base layer and of atleast one matt layer which essentially consists of a particularpolyethylene terephthalate copolymer, and also comprises a concentrationof from 3 to 40% of inert particles with diameter of from 0.3 to 20 μm.The specific copolymer is a processing aid which reduces the viscosityof the melt comprising the inert particles, permitting satisfactoryextrusion of this layer. Addition of the inert particles to theappropriate layer gives the film its mattness. The particles impairtransparency.

EP 0 144 978 describes a self-supporting oriented film made fromthermoplastic and bearing, on at least one of its two surfaces, acontinuous polyester coating which is applied in the form of an aqueousdispersion to the film prior to the final stretching step. The polyestercoating is composed of a condensation product of various monomers or oftheir derivatives capable of forming polyesters, for example isophthalicacid, aliphatic dicarboxylic acid, sulfomonomers, and aliphatic orcycloaliphatic glycol.

EP-A-0 620 245 describes films with improved heat resistance. Thesefilms comprise antioxidants suitable for scavenging free radicals formedwithin the film and degrading any peroxide formed. That specificationdoes not, however, provide any proposal as to how the UV resistance ofthese films may be improved.

The prior art described gives no indication that the films arethermoformable, or as to how at least one surface of the film may beprovided with low gloss while retaining high transparency, or that thefilm absorbs UV light, or that the film has high UV resistance.

It was an object of the present invention, therefore, to provide acoextruded biaxially oriented and transparent polyester film which hasat least one matt outer layer and is simple and cost-effective toproduce, and has the good physical properties of known films, andmoreover in particular absorbs UV light and has high UV resistance, andalso has good thermoformability. The film should also cause no problemsof disposal.

BRIEF DESCRIPTION OF THE INVENTION

The object is achieved by means of a biaxially oriented polyester filmwhich has a base layer preferably composed of at least 70% by weight ofa thermoplastic polyester and which is thermoformable, and comprises atleast on UV absorber, and has at least one matt outer layer whichcomprises a mixture or a blend made from two components I and II. Theinvention further relates to the use of the film and to a process forits production.

DETAILED DESCRIPTION OF THE INVENTION

High UV resistance means that sunlight or other UV radiation causes nodamage, or only extremely slight damage, to the film, and that the filmsare therefore suitable for outdoor applications and/or critical indoorapplications. In particular, it is intended that the films do not yellowafter a number of years of outdoor use, nor embrittle or show surfacecracking, nor have impaired mechanical properties. High UV resistancetherefore means that the film absorbs UV light and does not transmitlight until the visible region has been reached.

Adequate thermoformability means that, without uneconomic predrying, thefilm can be thermoformed on commercially available thermoformingmachinery to give complex and large-surface-area moldings.

The good mechanical properties include, inter alia, high modulus ofelasticity (E_(MD)>3200 N/mm²; E_(TD)>3500 N/mm²) and good values fortensile stress at break (in MD>100 N/mm²; in TD>130 N/mm²). Goodorientability includes the capability of the film to give excellentorientation during its production, both longitudinally and transversely,without break-offs.

For the purposes of the present invention, mixtures, particularly withregard to the outer layer(s), are mechanical mixtures produced from theindividual components. For this, the individual constituents aregenerally combined in the form of small-dimension compressed moldings,e.g. lenticular or bead-shaped pellets, and mixed with one another usinga suitable agitator. Another way of producing the mixture is for each ofthe components I and II in pellet form to be fed separately to theextruder for the outer layer according to the invention and for mixingto take place in the extruder and/or in the downstream systems fortransporting the melt.

For the purposes of the present invention a blend is an alloy-likecomposite of the individual components I and II which can no longer beseparated into the initial constituents. A blend has properties likethose of a homogeneous material and can be characterized by appropriateparameters.

According to the invention the film has at least two layers. Its layersare then a base layer B and the outer layer A according to theinvention. In another preferred embodiment of the invention the film hasa three-layer structure and has the outer layer A on one side of thelayer B and another layer C on the other side of the layer B. In thiscase the two layers A and C form the outer layers. These may beidentical or different. According to the invention, the UV absorber andthe flame retardant may be present in the outer layer(s) and/or the baselayer and/or in any intermediate layers present.

The base layer B of the film preferably is composed of at least 70% byweight of a thermoplastic polyester. Polyesters suitable for this arethose made from ethylene glycol and terephthalic acid (=polyethyleneterephthalate, PET), made from ethylene glycol andnaphthalene-2,6-dicarboxylic acid (=polyethylene 2,6-naphthalate, PEN),made from 1,4-bishydroxymethylcyclohexane and terephthalic acid(=poly-1,4-cyclohexanedimethylene terephthalate, PCDT), and also thosemade from ethylene glycol, naphthalene-2,6-dicarboxylic acid andbiphenyl-4,4′-dicarboxylic acid (=polyethylene 2,6-naphthalatebibenzoate, PENBB). Particular preference is given to polyesterscomposed of at least 90 mol %, in particular at least 95 mol %, ofethylene glycol units and terephthalic acid units or of ethylene glycolunits and naphthalene-2,6-dicarboxylic acid units. The remaining monomerunits derive from other aliphatic, cycloaliphatic or aromatic diols and,respectively, dicarboxylic acids, as may also be present in layer A(and/or layer C).

Examples of other suitable aliphatic diols are diethylene glycol,triethylene glycol and aliphatic glycols of the general formulaHO—(CH₂)_(n)—OH, where n is an integer from 3 to 6 (in particular1,3-propanediol, 1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol) andbranched aliphatic glycols having up to 6 carbon atoms. Among thecycloaliphatic diols, mention may be made of cyclohexanediols (inparticular 1,4-cyclohexanediol). Other suitable aromatic diols have, forexample, the formula HO—C₆H₄—X—C₆H₄—OH where X is —CH₂—, —C(CH₃)₂—,—C(CF₃)₂—, —O—, —S— or —SO₂—. Bisphenols of the formula HO—C₆H₄—C₆H₄—OHare also highly suitable.

It is important for the invention that the crystallizable thermoplastichas a diethylene glycol content (DEG content) of ≧1.0% by weight,preferably ≧1.2% by weight, in particular ≧1.3% by weight, and/or apolyethylene glycol content (PEG content) of ≧1.0% by weight, preferably≧1.2% by weight, in particular ≧1.3% by weight, and/or an isophthalicacid content (IPA content) of from 3 to 10% by weight.

The DEG content and/or PEG content of the polyester is advantageouslyset by the raw material producer during the polymerization process.

It was more than surprising that the fact that the diethylene glycolcontent and/or polyethylene glycol content and/or IPA content in thefilm is higher than in standard thermoplastics makes the film capable ofcost-effective thermoforming on commercially available thermoformingplants and leads to excellent reproduction of detail by the film.

Other preferred aromatic dicarboxylic acids are benzenedicarboxylicacids, naphthalenedicarboxylic acids (such as naphthalene-1,4- or-1,6-dicarboxylic acid), biphenyl-x,x′-dicarboxylic acids (in particularbiphenyl-4,4′-dicarboxylic acid), diphenylacetylene-x,x′-dicarboxylicacids (in particular diphenylacetylene-4,4′-dicarboxylic acid) andstilbene-x,x′-dicarboxylic acids. Among the cycloaliphatic dicarboxylicacids, mention may be made of cyclohexane dicarboxylic acids (inparticular cyclohexane-1,4-dicarboxylic acid). Particularly suitablealiphatic dicarboxylic acids are the C₃-C₁₉ alkanediacids, where thealkane moiety may be straight-chain or branched.

The polyesters of the invention may be prepared, for example, by thetransesterification process. The starting materials for this aredicarboxylic esters and diols, and these are reacted with the usualtransesterification catalysts, such as zinc salts, calcium salts,lithium salts, magnesium salts and manganese salts. The intermediatesare then polycondensed in the presence of widely used polycondensationcatalysts, such as antimony trioxide or titanium salts. The preparationmay equally take place by the direct esterification process in thepresence of polycondensation catalysts. This process starts directlyfrom the dicarboxylic acids and diols (Kunststoff Handbuch [PlasticsHandbook], Vol. III, Polyesters, Carl Hanser Verlag, Munich).

At least one matt outer layer of the multilayer film of the inventioncomprises a blend or mixture described in more detail below, made fromtwo components I and II, and, where appropriate, comprises additives.

Component I of the outer layer mixture or of the blend essentiallyconsists of a thermoplastic polyester, in particular a polyester of thistype as described in more detail for the base layer. For producing ahigh degree of mattness here, it has proven advantageous for thepolyester for component I of the outer layer to have a viscosity whichis per se relatively low. To describe the viscosities of the melts useis made of a modified solvent viscosity (SV or standard viscosity). Forcommercially available polyethylene terephthalates suitable forproducing biaxially oriented films the SVs are from 500 to 1200. Toobtain high mattness of the film for the purposes of the presentinvention it has proven advantageous for the SV of the polymers forcomponent I of the outer layer to be in the range from 500 to 800,preferably in the range from 500 to 750, particularly preferably in therange from 500 to 700.

Component II of the mixture or of the blend of the outer layer is apolyethylene terephthalate copolymer which is composed of thecondensation product of the following monomers or of their derivativescapable of forming polyesters:

A) from 65 to 95 mol % of isophthalic acid;

B) from 0 to 30 mol % of at least one aliphatic dicarboxylic acid withthe formulaHOOC(CH₂)_(n)COOH,

-   -   where    -   n is from 1 to 11, preferably 1 to 9;

C) from 5 to 15 mol % of at least one sulfomonomer comprising an alkalimetal sulfonate group on the aromatic moiety of a dicarboxylic acid; and

D) a copolymerizable aliphatic or cycloaliphatic glycol having from 2 to11 carbon atoms, preferably from 2 to 9 carbon atoms, in thestoichiometric amount necessary to form 100 mol % of condensate;

The percentages given are preferred values and are based in each case onthe total amount of the monomers forming component II.

The total amount of molar acid equivalents present are to be essentiallythe same as the total amount of molar glycol equivalents present.

Examples of dicarboxylic acids suitable as component B) of thecopolyesters are malonic, adipic, azelaic, glutaric, sebacic, suberic,succinic, and brassylic acid, and also mixtures of these acids or oftheir derivatives capable of forming polyesters. Of the acids mentioned,preference is given to sebacic acid.

Examples of sulfomonomers (component C) which contain a metal-sulfonategroup on the aromatic moiety of an aromatic dicarboxylic acid aremonomers of the following general formula:

In this formula

-   -   M is a monovalent cation of an alkali metal, preferably Na⁺, Li⁺        or K⁺,    -   Z is a trivalent aromatic radical, and    -   X and Y are carboxyl groups or polyester-forming equivalents.

Monomers of this type have been described in U.S. Pat. Nos. 3,563,942and 3,779,993. Examples of such monomers are the sodium salts ofsulfoterephthalic acid, 5-sulfoisophthalic acid, sulfophthalic acid,5-(p-sulfophenoxy)isophthalic acid, 5-sulfopropoxyisophthalic acid andsimilar monomers, and also their derivatives, such as the dimethylesters, capable of forming polyesters.

The term “derivatives capable of forming polyesters” here means reactionparticipants with groups capable of condensation reactions, inparticular transesterification reactions, to form polyester bonds.Groups of this type include carboxyl groups and also the lower alkylesters of these, e.g. dimethyl terephthalate, diethylterephthalate andnumerous other esters, halides or salts. The acid monomers arepreferably used in the form of dimethyl esters, since this gives bettercontrol of the condensation reaction.

Examples of glycols suitable as component D) are ethylene glycol,1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, 1,10-decanediol,cyclohexanedimethanol and similar substances. Preference is given to theuse of ethylene glycol.

The copolyesters of component II may be prepared by known polymerizationtechniques. The method is generally to combine the acid components withglycol and to apply heat in the presence of an esterification catalyst,and then to add a polycondensation catalyst (Kunststoff Handbuch[Plastics Handbook], Vol. VIII, Polyesters, Carl Hanser Verlag, Munich).

The relative proportions of components A, B, C and D used to prepare theblends or mixtures according to the invention have proven decisive forachieving the matt outer layer. For example, at least 65 mol % ofisophthalic acid (component A) must be present as acid component.Component A is preferably in the form of pure isophthalic acid, presentin amounts of from about 70 to 95 mol %.

For component B, any acid with the formula mentioned gives satisfactoryresults, and preference is given to adipic acid, azelaic acid, sebacicacid, malonic acid, succinic acid, glutaric acid and mixtures of theseacids. If component B is present in the composition the desirable amountwithin the range given is preferably from 1 to 20 mol %, based on theacid components of the mixture I.

The amount of the glycol component present is approximatelystoichiometric.

The copolyesters of component II that are suitable for the purposes ofthe invention also have an acid value of less than 10, preferably offrom 0 to 3, an average molecular weight of below about 50,000 and an SVof from about 30 to 700, preferably from about 350 to 650.

The ratio (by weight) of the two components I and II of the outer layermixture or of the blend may vary within wide limits and depends on theapplication intended for the multilayer film. The ratio of components Iand II is preferably from I:II=10:90 to I:II=95:5, preferably fromI:II=20:80 to I:II=95:5 and in particular from I:II=30:70 to I:II=95:5.

Light, in particular the ultraviolet content of solar radiation, i.e.,the wavelength region from 280 to 400 nm, induces degradation inthermoplastics, as a result of which their appearance changes due tocolor change or yellowing, and there is also an adverse effect onmechanical/physical properties.

Inhibition of this photooxidative degradation is of considerableindustrial and economic importance, since otherwise there are drasticlimitations on the applications of many thermoplastics.

The absorption of UV light by polyethylene terephthalates, for example,starts at below 360 nm, increases markedly below 320 nm, and is verypronounced at below 300 nm. Maximum absorption occurs at between 280 and300 nm.

In the presence of oxygen it is mainly chain cleavage which occurs, butthere is no crosslinking. The predominant photooxidation products inquantity terms are carbon monoxide, carbon dioxide, and carboxylicacids. Besides direct photolysis of the ester groups, consideration hasto be given to oxidation reactions which likewise form carbon dioxidevia peroxide radicals.

In the photooxidation of polyethylene terephthalates there can also becleavage of hydrogen at the position α to the ester groups, givinghydroperoxides and decomposition products of these, and this may beaccompanied by the chain cleavage (H. Day, D. M. Wiles: J. Appl. Polym.Sci. 16, 1972, p. 203).

UV stabilizers, i.e. light stabilizers which are UV absorbers, arechemical compounds which can intervene in the physical and chemicalprocesses of light-induced degradation. Carbon black and other pigmentscan give some protection from light. However, these substances areunsuitable for transparent films, since they cause discoloration orcolor change. The only compounds suitable for transparent matt films arethose organic or organometallic compounds which produce no, or onlyextremely slight, color or color change in the thermoplastic to bestabilized, that is to say those which are soluble in the thermoplastic.

For the purposes of the present invention, UV stabilizers suitable aslight stabilizers are those which absorb at least 70%, preferably 80%,particularly preferably 90%, of the UV light in the wavelength regionfrom 180 to 380 nm, preferably from 280 to 350 nm. These areparticularly suitable if they are thermally stable in the temperaturerange from 260 to 300° C., that is to say they do not decompose and donot cause evolution of gases. Examples of UV stabilizers suitable aslight stabilizers are 2-hydroxybenzophenones, 2-hydroxybenzotriazoles,organonickel compounds, salicylic esters, cinnamic ester derivatives,resorcinol monobenzoates, oxanilides, hydroxybenzoic esters, andsterically hindered amines and triazines, and among these oxanilides,hydroxybenzoic esters, and sterically hindered amines and triazines, andamong these preference is given to the 2-hydroxybenzotriazoles and thetriazines.

In one particularly preferred embodiment, the film of the inventioncomprises from 0.01 to 5.0% by weight of2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-hexyloxyphenol of the formula

or from 0.01 to 5.0% by weight of2,2′-methylenebis(6-(2H-benzotriazol-2-yl)-4-(1,1,2,2-tetramethylpropyl)phenol)of the formula

It is also possible in one preferred embodiment to use a mixture ofthese two UV stabilizers or a mixture of at least one of these two UVstabilizers with other UV stabilizers, the total concentration of lightstabilizer preferably being from 0.01 to 5.0% by weight, based on theweight of crystallizable polyethylene terephthalate.

The UV stabilizer(s) is/are preferably present in the outer layer(s). Ifrequired, UV stabilizer may also be provided in the core layer.

It was highly surprising that use of the abovementioned UV stabilizersin films gave the desired result. The skilled worker would probablyfirst have attempted to achieve a certain degree of UV resistance by wayof an antioxidant, but would have found that the film rapidly yellows onweathering.

In the knowledge that UV stabilizers absorb UV light and thereforeprovide protection, the skilled worker would be likely to have usedcommercially available UV stabilizers. It would then have been foundthat

-   -   the UV stabilizer has unsatisfactory thermal stability and at        temperatures of from 200 to 240° C. decomposes and causes        evolution of gases, and    -   large amounts (from about 10 to 15% by weight) of UV stabilizer        have to be incorporated so that the UV light is absorbed and        damage to the film is therefore prevented.

At these high concentrations it would have been found that the film isyellow even immediately after its production, with Yellowness Indexdifferences (YI) around 25. It would also have been found that itsmechanical properties are adversely affected. Orientation would haveproduced exceptional problems, for example

-   -   break-offs due to unsatisfactory strength, i.e. modulus of        elasticity too low,    -   die deposits, causing profile variations,    -   roller deposits from the UV stabilizer, causing impairment of        optical properties (defective adhesion, non-uniform surface),        and    -   deposits in scratching frames or heat-setting frames, dropping        onto the film.

It was therefore more than surprising that even low concentrations ofthe UV stabilizer achieve excellent UV protection. It was verysurprising that, together with this excellent UV protection

-   -   within the accuracy of measurement, the Yellowness Index of the        film is unchanged from that of an unstabilized film;    -   there was no evolution of gases and there were no die deposits        or frame condensation, and the film therefore has excellent        optical properties and excellent profile and layflat, and    -   the UV-resistant film has excellent stretchability, and can        therefore be produced in a reliable and stable manner on        high-speed film lines at speeds of up to 420 m/min.

It was surprising that a relatively high diethylene glycol contentand/or polyethylene glycol content in comparison with standard polyesterpermits oriented PET films to be thermoformed.

The thermoforming process generally encompasses the steps of predrying,heating, molding, cooling, demolding, and heat-conditioning.Surprisingly, it was found that the films of the invention can bethermoformed without predrying. The costs of the forming process aredrastically reduced by this advantage over thermoformable polycarbonatefilms or thermoformable polymethyl methacrylate films, for whichpredrying times of from 10 to 15 hours at temperatures of from 100 to120° C. are required, depending on thickness.

Examples of the process parameters found for thermoforming were asfollows

Step of process Film of invention Predrying Not required Moldtemperature ° C. 100-160 Heating time <5 sec per 10 μm of thickness Filmtemperature during 160-200 shaping ° C. Possible orientation 1.5-2.0factor Reproduction of detail Good Shrinkage % <1.5

The base layer and/or the outer layer(s) and/or the intermediate layersmay also comprise conventional additives, such as stabilizers andantiblocking agents. They are usefully added to the polymer or to thepolymer mixture before melting. Examples of stabilizers used arephosphorus compounds, such as phosphoric acid or its esters. Typicalantiblocking agents (also termed pigments in this context) are inorganicand/or organic particles, for example calcium carbonate, amorphoussilica, talc, magnesium carbonate, barium carbonate, calcium sulfate,barium sulfate, lithium phosphate, calcium phosphate, magnesiumphosphate, alumina, LiF, the calcium, barium, zinc or manganese salts ofthe dicarboxylic acids used, carbon black, titanium dioxide, kaolin andcrosslinked polystyrene particles or crosslinked acrylate particles.

Mixtures of two or more different antiblocking agents or mixtures ofantiblocking agents of the same composition but different particle sizemay also be used as additives. The particles may be added to theindividual layers in the usual concentrations, e.g. as a glycolicdispersion during the polycondensation or via masterbatches duringextrusion. Pigment concentrations which have proven particularlysuitable are from 0.0001 to 10% by weight, based on the layers in whichthey are present. Adding these particles to the outer layer(s) gives thefurther advantageous possibility of varying the degree of mattness ofthe film. Increasing the pigment concentration is generally alsoassociated with an increase in the degree of mattness of the film. Adetailed description of suitable antiblocking agents is found in EP-A 0602 964, for example.

The present invention also provides a process for producing this film.It encompasses the following steps:

a) producing a film from base and outer layer(s), and, whereappropriate, intermediate layers, by coextrusion,

b) biaxial orientation of the film, and

c) heat-setting of the oriented film.

To produce the outer layer(s) according to the invention it is useful tofeed pellets of mixing component I and pellets of mixing component II inthe desired mixing ratio, and, where appropriate, the UV masterbatch,directly to the extruder. It has proven useful to use a twin-screwextruder for extruding the matt outer layer(s) according to theinvention, as described, for example, in EP 0 826 478. The materials canbe melted and extruded at about 300° C. and with a residence time ofabout 5 min. The transesterification reactions which can occur in theextruder under these conditions can form other copolymers from thehomopolymers and the copolymers.

The UV absorber may also advantageously be incorporated into thepolymers of the outer layers and/or of the base layer before thepolymers leave the producer of the raw material.

It is particularly preferable to add the UV absorber by way ofmasterbatch technology directly during film production. The UV absorberis dispersed in a solid carrier. Carrier materials which may be used arecertain resins, the outer layer polymer and/or the base layer polymeritself, or else other polymers which are sufficiently compatible withthe thermoplastic.

In masterbatch technology it is important that the grain size and thebulk density of the masterbatch are similar to the grain size and thebulk density of the polymers of the base layer and/or of the outerlayer, so that distribution of the UV absorber can be homogeneous andtherefore UV resistance can be homogeneous.

The polymers for the base layer are usefully fed via another extruder.Any foreign bodies or contamination present can be filtered out from thepolymer melt prior to extrusion. The melts are then extruded via acoextrusion die to give flat melt films and the layers are mutuallysuperposed. The multilayer film is then drawn off and solidified withthe aid of a chill roll and, if desired, of other rolls.

The biaxial orientation procedure is generally carried out in successionor simultaneously. For stretching in succession it is preferable for thefirst orientation to be longitudinal (i.e. in the machine direction) andfor this to be followed by transverse orientation (i.e. perpendicularlyto the machine direction). This causes orientation of the molecularchains. The longitudinal orientation process can be carried out with theaid of two rolls running at different speeds corresponding to thedesired stretching ratio. For the transverse orientation process use isgenerally made of an appropriate tenter frame. For the simultaneousstretching process, the film is stretched simultaneously in longitudinaland transverse directions in a tenter frame.

The temperature at which the orientation process is carried out may varyover a relatively wide range and depends on the properties desired inthe film. The longitudinal stretching process is generally carried outat from about 80 to 135° C., and the transverse stretching process atfrom about 90 to 150° C. The longitudinal stretching ratio is generallyfrom 2.5:1 to 6:1, preferably from 3:1 to 5.5:1. The transversestretching ratio is generally from 3.0:1 to 5.0:1, preferably from 3.5:1to 4.5:1. If desired, the transverse stretching process may be followedby a further longitudinal orientation process and even a furthertransverse orientation process.

In the heat-setting process which follows, the film is held at atemperature of from about 150 to 250° C. for from about 0.1 to 10 s. Thefilm is then wound up in a usual manner.

At least one of the surfaces of the film may, furthermore, be coated insuch a way that the coating on the finished film has a thickness of from5 to 100 nm, preferably from 20 to 70 nm, in particular from 30 to 50nm. The coating is preferably applied in-line, i.e. during thefilm-production process, usefully prior to the transverse stretchingprocess. A particularly preferred application method is reversegravure-roll coating, which can apply extremely homogeneous coatings ofthe thicknesses mentioned. The coatings are preferably applied in theform of solutions, suspensions or dispersions, particularly preferablyas aqueous solution, suspension or dispersion. The coatings mentionedgive the film surface an additional function, for example render thefilm sealable, printable, metallizable, sterilizable or antistatic, orimprove the aroma barrier, or allow adhesion to materials which wouldotherwise not adhere to the surface of the film (for examplephotographic emulsions). Examples of substances/compositions which giveadditional functionality are:

Acrylates, as described, for example, in WO 94/13476, ethylene-vinylalcohols, PVDC, water glass (Na₂SiO₄), hydrophilic polyesters (PET/IPApolyesters as described, for example, in EP-A-0 144 878, U.S. Pat. No.4,252,885 or EP-A-0 296 620 and containing the sodium salt of5-sulfoisophthalic acid), vinyl acetates, as described, for example, inWO 94/13481, polyvinyl acetates, polyurethanes, the alkali-metal oralkaline-earth-metal salts of C₁₀-C₁₈ fatty acids, butadiene copolymerswith acrylonitrile or methyl methacrylate, methacrylic acid, acrylicacid or esters thereof.

The substances/compositions mentioned are applied in the form of dilutesolution, emulsion or dispersion, preferably aqueous solution, emulsionor dispersion, to one or both surfaces of the film, and the solvent isthen evaporated. If the coatings are applied in-line prior to thetransverse stretching process, the heat treatment during the transversestretching process and the subsequent heat-setting is usually sufficientto evaporate the solvent and to dry the coating. The dried coatings thenhave the desired thicknesses mentioned above.

The films may, furthermore, be coated, preferably in an off-line processusing metals, such as aluminum, or ceramic materials, such as SiO_(x) orAl_(x)O_(y). This improves in particular their gas-barrier properties.

The polyester film of the invention preferably also comprises a secondouter layer C. The structure, thickness and composition of a secondouter layer may be selected independently of the outer layer alreadypresent. The second outer layer may also comprise the abovementionedpolymers, UV absorbers, and/or polymer mixtures for the base layer orthe first outer layer according to the invention, but these do not haveto be identical with those of the first outer layer. The second outerlayer may also comprise other common outer layer polymers, which mayalso have been provided with UV absorbers.

Between the base layer and the outer layer(s) there may also, ifdesired, be an intermediate layer. It may be composed of the polymersdescribed for the base layers. In a particularly preferred embodiment itis composed of the polyester used for the base layer. It may alsocomprise the conventional additives described and the UV absorber. Thethickness of the intermediate layer is generally greater than 0.3 μm andis preferably from 0.5 to 15 μm, in particular from 1.0 to 10 μm.

The thickness of the outer layer(s) is generally greater than 0.1 μm andpreferably from 0.2 to 5 μm, in particular from 0.2 to 4 μm, and theouter layers may have identical or different thicknesses.

The overall thickness of the polyester film of the invention may varywithin wide limits and depends on the application intended. It ispreferably from 4 to 500 μm, in particular from 5 to 450 μm, preferablyfrom 6 to 300 μm, and the base layer preferably makes up a proportion offrom about 40 to 90% of the overall thickness.

Weathering tests have shown that, even after from 5 to 7 years in anoutdoor application (extrapolated from the weathering tests), theUV-resistant films of the invention generally show no increase inyellowing, no embrittlement, no loss of surface gloss, no surfacecracking, and no impairment of mechanical properties.

Another advantage is that the costs of producing the film of theinvention are not significantly greater than those for a film made fromstandard polyester raw materials. The other properties of the film ofthe invention relevant to its processing and use remain essentiallyunchanged or are even improved. In addition, it has been ensured that aproportion of up to 50% by weight, preferably from 10 to 50% by weightof recycled material, based in each case on the total weight of thefilm, can be reused in producing the film, without any significantadverse effect on its physical properties.

The film has excellent suitability for packaging food and otherconsumable items which, in both these cases, are sensitive to lightand/or to air, and also for producing moldings which are to provide UVprotection or to be UV-resistant.

In summary, the film of the invention has good thermoformability,impermeability to UV light, high UV resistance, and low gloss, inparticular low gloss on film surface A, and relatively low haze. It alsohas good winding and processing performance. The good inscribability ofthe outer layer according to the invention with ballpoint pens,felt-tips or fountain pens is also worthy of mention.

The gloss of film surface A is lower than 70. In a preferred embodimentthe gloss of this side is lower than 60, and in a particularly preferredembodiment it is lower than 50. The nature of this surface of the filmis therefore particularly effective for sales promotion and it thereforehas very particular suitability as the outward-facing surface ofpackaging.

The haze of the film is less than 40%. In a preferred embodiment it isless than 35%, and in a particularly preferred embodiment it is lessthan 30%. The comparatively low haze of the film (compared with a mattmonofilm, see comparative example) means that the film can, for example,be reverse-printed, or viewing windows can be incorporated throughwhich, for example, the contents can be clearly discerned.

The combination of advantageous properties gives the film of theinvention excellent suitability for a wide variety of applications, forexample for interior decoration, for the construction of exhibitionstands, for exhibition requisites, as displays, for placards, forprotective glazing of machinery or of vehicles, in the lighting sector,in the fitting out of shops or of stores, as a promotional requisite, alaminating medium, for greenhouses, roofing systems, exterior cladding,protective coverings, applications in the construction sector, andilluminated advertising profiles, blinds, and electrical applications,and also thermoforming applications.

Other application sectors are the production of labels and as a releasefilm or stamping foil.

The table below (table 1) once again gives the most important filmproperties of the invention.

TABLE 1 Range according Particularly Method of to the inventionPreferred preferred Unit measurement Gloss of side A <70 <60 <50 DIN 67530 (60° angle of measurement) Haze <40 <35 <30 % ASTM D1003-52Coefficient of friction: Side A <0.6 <0.55 <0.50 DIN 53 375 with respectto itself Side C <0.5 <0.55 <0.55 and, respectively, side B with respectto itself Average roughness R_(a) 200-600 230-550 250-530 nm DIN 4768with a Side A cut-off of 0.25 mm Yellowness Index (YI) <30 <20 <10 DIN6167 High UV resistance yes Wavelength from which >350 >360 nmpermeability to UV light begins Thermoformability Yes Orientation factorduring 1.5-2.0 thermoforming Reproduction of detail during goodthermoforming

The following methods were used to characterize the raw materials andthe films:

Methods

DIN=Deutsches Institut für Normung [German Institute forStandardization]

ISO=International Organization for Standardization

-   ASTM=American Society for Testing and Materials

DEG Content/PEG Content, and IPA Content

DEG content, PEG content, and IPA content is determined by gaschromatography after saponification in methanolic KOH and neutralizationwith aqueous HCl.

SV (DCA), and IV (DCA)

Standard viscosity SV (DCA) is measured by a method based on DIN 53726in dichloroacetic acid.

Intrinsic viscosity (IV) is calculated as follows from standardviscosity

-   -   IV (DCA)=6.67·10⁻⁴ SV (DCA)+0.118

Coefficient of Friction

Coefficient of friction was determined to DIN 53 375, 14 days afterproduction.

Surface Tension

Surface tension was determined by what is known as the ink method (DIN53 364).

Haze

Film haze was measured to ASTM D1003-52. Hölz haze was determined by amethod based on ASTM D1003-52, but in order to utilize the mosteffective measurement range, measurements were made on four pieces offilm laid one on top of the other, and a 1° slit diaphragm was usedinstead of a 4° pinhole.

Gloss

Gloss was determined to DIN 67 530. The reflectance was measured, thisbeing an optical value characteristic of a film surface. Based on thestandards ASTM D523-78 and ISO 2813, the angle of incidence was set at20° or 60°. A beam of light hits the flat test surface of the set angleof incidence and is reflected and/or scattered by this surface. Aproportional electrical variable is displayed representing light rayshitting the photoelectronic detector. The value measured isdimensionless and must be stated together with the angle of incidence.

Roughness

Roughness R_(a) of the film was determined to DIN 4768 with a cut-off of0.25 mm.

Mechanical Properties

Modulus of elasticity and tensile stress at break, and tensile strain atbreak, are measured longitudinally and transversely to ISO 527-1-2.

Weathering (Bilateral), and UV Resistance:

UV resistance is tested as follows to the ISO 4892 test specification:

Test equipment Atlas Ci65 Weather-Ometer Test conditions ISO 4892, i.e.artificial weathering Irradiation time 1000 hours (per side) Irradiation0.5 W/m², 340 nm Temperature 63° C. Relative humidity 50% Xenon lampinternal and external filter made from borosilicate Irradiation cycles102 minutes of UV light, then 18 minutes of UV light with water sprayedonto the specimens, then again 102 minutes of UV light, etc.

Numerical values <0.6 are negligible and mean that there is nosignificant color change.

Yellowness Index

Yellowness Index (YI) is the deviation from colorlessness in the“yellow” direction and is measured to DIN 6167. Yellowness Index values(YI)<5 are not visually detectable.

The examples and comparative examples below use films of varyingthickness, produced on the extrusion line described.

All of the films were bilaterally weathered to test specification ISO4892, in each case for 1000 hours per side, using the Atlas Ci65Weather-Ometer, and then tested for mechanical properties, YellownessIndex (YI), surface defects, light-transmittance, and gloss.

The examples below illustrate the invention.

EXAMPLE 1

a) Preparation of component II for the outer layer mixture of theinvention.

A copolyester containing about 90 mol % of isophthalic acid and 10 mol %of the sodium salt of 5-sulfoisophthalic acid, as acid component, and100 mol % of ethylene glycol, as glycol component, was prepared by thefollowing method:

A stainless-steel reaction vessel of 2 l capacity, equipped with ananchor stirrer, a thermal element for measuring the temperature of thevessel contents, an 18-inch Claisen/Vigreux distillation column withcondenser and receiving vessel, an inlet opening and a heating jacket,was preheated to 190° C. and flushed with nitrogen. 1065.6 g of dimethylisophthalate, 180.6 g of the sodium salt of dimethyl 5-sulfoisophthalateand 756.9 g of ethylene glycol were placed in the vessel. A buffer(Na₂CO₃.10H₂O-0.439 g) and a transesterification catalyst(Mn(OAc)₂.4H₂O-0.563 g, Ac=Acetate) were also placed in the vessel. Themixture was heated with stirring, whereupon methanol distilled off.During the distillation the temperature in the vessel was graduallyincreased to 250° C. When the distillate weight corresponded to thetheoretical methanol yield, an excess of ethylene glycol solutioncomprising 0.188 g of phosphorous acid was added. The distillationcolumn was replaced by a curved vapor take-off with receiving vessel. 20g of pure ethylene carbonate were added to the reaction mixture,whereupon vigorous evolution of gas (CO₂) began immediately. CO₂evolution subsided after about 10 min. A reduced pressure of 240 mm ofHg was then applied, and the polycondensation catalyst (0.563 g of Sb₂O₃slurried in ethylene glycol) was added. The reaction mixture was stirredfor 10 min while maintaining the reduced pressure of 240 mm of Hg afterwhich the pressure was further reduced from 240 to 20 mm of Hg in stepsof 10 mm of Hg/min. As soon as the pressure in the system had beenreduced to 20 mm of Hg, the temperature in the vessel was raised from250° C. to 290° C. at a rate of 2° C./min. When the temperature in thevessel had reached 290° C. the stirrer speed was throttled back and thepressure reduced to not more than 0.1 mm of Hg. At this juncture aread-out was obtained from the stirrer motor using an ammeter. Theviscosity of the polymer was controlled by allowing the polycondensationto proceed in accordance with set values for the change in the amperevalue from the stirrer motor of (in each case) 2-3 A. When the desiredmolecular weight had been achieved, nitrogen pressure was applied to thevessel to expel the liquid polymer from the outlet in the base of thevessel into an ice-water quenching bath.

B) Preparation of the mixture for outer layer A according to theinvention 75% by weight of component I (polyethylene terephthalate withSV of 680) were fed with 15% by weight of component II and 10% by weightof a masterbatch which comprises the UV stabilizer to the inlet hopperof a twin-screw extruder and the two components were extruded togetherat about 300° C. and fed to the outer layer channel A of a coextrusiondie.

The masterbatch is composed of 5% by weight of2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-hexyloxyphenol (®TINUVIN 1577 fromCiba-Geigy) as UV absorber and 95% by weight of polyethyleneterephthalate.

At the same time, polyethylene terephthalate chips which have DEGcontent of 1.6% by weight and PEG content of 1.7% by weight were driedat 160° C. to a residual moisture level less than 50 ppm and fed to theextruder for the base layer. Polyethylene terephthalate chips which haveDEG content of 1.6% by weight and PEG content of 1.7% by weight were fedwith UV masterbatch and a filler to the extruder for the outer layer C.Coextrusion followed by stepwise longitudinal and transverse orientationwas then used to produce a transparent three-layer film with ABCstructure and an overall thickness of 12 μm. The thickness of each outerlayer was 1.5 μm.

Base layer B: 95% by weight of polyethylene terephthalate with SV of800, DEG content of 1.6% by weight, and PEG content of 1.7% by weight 5% by weight of masterbatch made from 99% by weight of polyethyleneterephthalate and 1.0% by weight of silica particles (® Sylobloc 44 Hfrom Grace) with average particle size 4.5 μm. Outer layer A: 75% byweight of component I, 15% by weight of component II, and 10% by weightof UV masterbatch made from 5% by weight of ® TINUVIN 1577 and 95% byweight of polyethylene terephthalate. Outer layer C: 80% by weight ofpolyethylene terephthalate with SV of 800, DEG content of 1.6% byweight, and PEG content of 1.7% by weight 10% by weight of masterbatchmade from 99% by weight of polyethylene terephthalate and 1.0% by weightof silica particles (® Sylobloc 44 H from Grace) with average particlesize 4.5 μm 10% by weight of UV masterbatch made from 5% by weight of® TINUVIN 1577 and 95% by weight of polyethylene terephthalate.

The individual steps of the process were:

Longitudinal Temperature: 85-135° C. stretching Longitudinal 4.0:1stretching ratio: Transverse Temperature: 85-135° C. stretchingTransverse 4.0:1 stretching ratio: Setting Temperature:   230° C.

EXAMPLE 2

Using a method based on example 1, a three-layer film of total thickness12 μm was produced by coextrusion. Only the composition of the outerlayer A was changed:

Outer Layer A:

70% by weight of component I

20% by weight of component II, and

10% by weight of UV masterbatch.

EXAMPLE 3

A coextruded film with the specification of example 1, the compositionof the outer layer A being as follows:

65% by weight of component I

25% by weight of component II, and

10% by weight of UV masterbatch.

EXAMPLE 4

A coextruded film with the specification of example 1, the compositionof the outer layer A being as follows:

55% by weight of component I

35% by weight of component II, and

10% by weight of UV masterbatch.

COMPARATIVE EXAMPLE

A monofilm was produced, its composition being the same as the outerlayer A of example 3, but the film comprises no UV absorber and does nothave the relatively high DEG content, and nor is any PEG present in thefilm. The film surfaces had the required mattness, but the film did notmeet the requirements placed upon it, because its haze was excessive. Itwas also very difficult to produce the film by a process which wasreliable and therefore cost-effective.

The film is moreover not UV-resistant and transmits harmful UV light.After 1000 hours of weathering the film exhibits cracking andembrittlement phenomena, and also visible yellowing.

The thermoformability of the film was inadequate.

The results of the examples and comparative example (CE) are given intable 2 below:

TABLE 2 Film Outer layer Gloss (60° angle Permeability Example thicknessthickness A/C Film of measurement) to radiation No. (μm) (μm) structureSide A Side C Haze (nm) 1 12 1.5/1.5 ABC 65 175 25 >360 2 12 1.5/1.5 ABC55 175 26 >360 3 12 1.5/1.5 ABC 45 175 28 >360 4 12 1.5/1.5 ABC 35 17530 >360 CE 12 A 35 160 70 >280

After 1000 hours of weathering using the Atlas Ci65 Weather-Ometer, thefilms of examples 1 to 4 exhibit no embrittlement, no cracking, andYellowness Indices <10. The film from examples 1 to 4 can bethermoformed to give moldings, without predrying, on commerciallyavailable thermoforming machinery, e.g. from the company Illig(Germany). The reproduction of detail in the thermoformed parts isexcellent, and their surface is homogeneous.

1. A polyester film which has a base layer (B) made from a thermoplasticpolyester and has at least one matt outer layer (A), and wherein thefilm comprises at least one UV absorber, wherein the matt outer layer(A) comprises a mixture or a blend or a mixture and a blend made fromtwo components I and II, wherein component I is essentially apolyethylene terephthalate homopolymer or polyethylene terephthalatecopolymer or a mixture made from polyethylene terephthalate homopolymeror polyethylene terephthalate copolymer, and component II is a polymerwhich contains at least one sulfonate group.
 2. A polyester film asclaimed in claim 1, wherein the film comprises at least one intermediatelayer between the base layer (B) and the outer layer (A).
 3. Thepolyester film as claimed in claim 1, which has an additional outerlayer (C) arranged on the opposite surface of base layer (B) on whichthe matt outer layer (A) is arranged and which film has an A-B-C layerstructure, wherein the outer layers A and C may be identical ordifferent.
 4. The polyester film as claimed in claim 1, wherein the baselayer (B) is composed of at least 70% by weight of a thermoplasticpolyester.
 5. The polyester film as claimed in claims 1, wherein thethermoplastic polyester comprises polyethylene terephthalate or apolyester composed of at least 90 mol % of ethylene glycol units andterephthalic acid units or of ethylene glycol units andnaphthalene-2,6-dicarboxylic acid units.
 6. The polyester film asclaimed in claim 1, wherein component II of the mixture or of the blendof the outer layer (A) is a copolymer which is composed of thecondensation product of isophthalic acid and of at least onesulfomonomer which has an alkali metal sulfonate group on the aromaticmoiety of a dicarboxylic acid, and of a copolymerizable aliphatic orcycloaliphatic glycol, or of derivatives of these which are capable offorming polyesters.
 7. The polyester film as claimed in claim 6, whereinthe copolymer is composed of the condensation product of isophthalicacid and of of at least one aliphatic dicarboxylic acid of the formulaHOOC(CH₂)_(n)COOH, where n=from 1 to 11, and of at least onesulfomonomer which has an alkali metal sulfonate group on the aromaticmoiety of a dicarboxylic acid, and of a copolymerizable aliphatic orcycloaliphatic glycol, or of derivatives of these which are capable offorming polyesters.
 8. The polyester film as claimed in claim 6 or 7,wherein the monomers used to form component II are present in thefollowing molar ratios: isophthalic acid from 65 to 95 mol %, aliphaticdicarboxylic acid from 0 to 30 mol %, sulfomonomer from 5 to 15 mol %,and the stoichiometric amount of glycol needed to form 100 mol %.
 9. Thepolyester film as claimed in claim 1, wherein the UV absorber is presentin the base layer or in the outer layers or in the base layer and in theouter layers.
 10. The polyester film as claimed in claim 1, wherein theUV absorber comprises 2-hydroxybenzotriazoles or triazines or a mixtureof these UV absorbers.
 11. The polyester film as claimed in claim 1,wherein the UV absorber comprises2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-hexyloxyphenol or2,2′-methylene-bis-6-(2H-benzotriazol-2-yl)-4-(1,1,2,2-tetra-methylpropyl)phenolor a mixture of these UV absorbers or a mixture of these UV absorberswith other UV absorbers.
 12. The polyester film as claimed in claim 1,wherein the concentration of the UV absorber is from 0.01 to 5% byweight, based on the weight of the layer in which it is present.
 13. Thepolyester film as claimed in claim 1, which additionally has afunctional coating on at least one surface.
 14. A process for producingthe polyester film as claimed in claim 1, wherein the starting materialsrequired for producing the base and outer layer are coextruded by way ofone or more extruders through a coextrusion die and the resultant filmis biaxially oriented and heat-set.
 15. The process as claimed in claim14, wherein a UV absorber is added by way of masterbatch technology. 16.A method of making a molding which comprises converting a polyester filmas claimed in claim 1 into a molding.
 17. A molding comprising apolyester film as claimed in claim
 1. 18. A polyester film which has abase layer (B) made from a thermoplastic polyester and has at least onematt outer layer (A), and wherein the film comprises at least one UVabsorber, wherein the matt outer layer (A) comprises a mixture or ablend or a mixture and a blend made from two components I and II,wherein component I is essentially a polyethylene terephthalatehomopolymer or polyethylene terephthalate copolymer or a mixture madefrom polyethylene terephthalate homopolymer or polyethyleneterephthalate copolymer, and component II is a polymer which contains atleast one sulfonate group, wherein the polyethylene terephthalate of thebase layer (B) has a diethylene glycol content or a polyethylene glycolcontent or a diethylene glycol content and a polyethylene glycol contentgreater than 1.3% by weight.
 19. A polyester film which has a base layer(B) made from a thermoplastic polyester and has at least one matt outerlayer (A), and wherein the film comprises at least one UV absorber,wherein the matt outer layer (A) comprises a mixture or a blend or amixture and a blend made from two components I and II, wherein componentI is essentially a polyethylene terephthalate homopolymer orpolyethylene terephthalate copolymer or a mixture made from polyethyleneterephthalate homopolymer or polyethylene terephthalate copolymer, andcomponent II is a polymer which contains at least one sulfonate group,wherein the polyethylene terphthalate of the base layer (B) has adiethylene glycol content or a polyethylene glycol content or adiethylene glycol content and a polyethylene glycol content of from 1.6to 5% by weight.
 20. A thermoformable, biaxially oriented polyester filmwhich has a base layer (B) made from a thermoplastic polyester and hasat least one matt outer layer (A), and wherein the film comprises atleast one UV absorber, wherein the matt outer layer (A) comprises amixture or a blend or a mixture and a blend made from two components Iand II, wherein component I is essentially a polyethylene terephthalatehomopolymer or polyethylene terephthatale copolymer or a mixture madefrom polyethylene terephthalate homopolymer or polyethyleneterephthalate copolymer, and component II is a polymer which contains atleast one sulfonate group, wherein the polyethylene terephthalate of thebase layer (B) has at least one of (i) a diethylene glycol content or(ii) a polyethylene glycol content of at least about 1.0% by weight. 21.A thermoformable, biaxially oriented polyester film which has a baselayer (B) made from a thermoplastic polyester and has at least one mattouter layer (A), and wherein the film comprises at least one UVabsorber, wherein the matt outer layer (A) comprises a mixture or ablend or a mixture and a blend made from two components I and II,wherein component I is essentially a polyethylene terephthalatehomopolymer or polyethylene terephthalate copolymer or a mixture madefrom polyethylene terephthalate hompolymer or polyethylene terephthalatecopolymer, and component II is a polymer which contains at least onesulfonate group, wherein the polyethylene terephthalate of the baselayer (B) has a diethylene glycol content of at least about 1.3% byweight and a polyethylene glycol content of at least about 1.3% byweight.
 22. A thermoformable, biaxially oriented polyester film whichhas a base layer (B) made from a thermoplastic polyester and has atleast one matt outer layer (A), and wherein the film comprises at leastone UV absorber, wherein the matt outer layer (A) comprises a mixture ora blend or a mixture and a blend made from two components I and II,wherein component I is essentially a polyethylene terephthalatehomopolyer or polyethylene terephthalate copolymer or a mixture madefrom polyethylene terephthalate homopolymer or polyethyleneterephthalate copolymer, and component II is a polymer which contains atleast one sulfonate group, wherein the at least one UV absorber is amixture of 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-hexyloxyphenol and2,2-methylenebis(6-(2H-benzotriazol-2-yl)-4-(1,1,2,2,-tetramethylpropyl)-phenol.23. A thermoformable biaxially oriented polyester film which has a baselayer (B) made from a thermoplastic polyester disposed between first andsecond outer layers. wherein said first outer layer is a matt layercomprising at least one UV absorber within a mixture or a blend or amixture and a blend made from two components I and II, wherein componentI is essentially a polyethylene terephthalate homopolymer orpolyethylene terephthalate copolymer or a mixture made from polyethyleneterephthalate homopolymer or polyethylene terephthalate copolymer, andcomponent II is a polymer which contains at least on sulfonate group andsaid second outer layer comprises at least one UV absorber, and UVabsorber is absent from the base layer (B).